Using long-term monitoring data to detect changes in macroinvertebrate species composition in the harbour of Ghent (Belgium)

The macroinvertebrate community of the harbour of Ghent was studied by analysing 135 samples taken at different locations from 1990 until 2008. The results showed that current Crustacea and Mollusca communities were mainly represented, in terms of abundances, by alien species. In total, seven alien and four indigenous crustacean species were found. Mollusc diversity was higher, with a total of 14 species, four of which were alien. Before 1993, no alien macroinvertebrates were present in the harbour of Ghent. Afterwards, the number of alien taxa increased, whereas the number of native taxa remained stable. Macroinvertebrate diversity was very low at the beginning of the 1990s, but increased due to the improvement of the chemical water quality achieved by sanitation and stricter environmental laws. This was reflected by an increase in dissolved oxygen and a decrease in nutrients, allowing more sensitive species to establish. Due to intensive international boat traffic, the brackish water conditions and the low species diversity, the harbour of Ghent is highly vulnerable for invasions. Stronger regulations and a better understanding of the contribution of shipping, shortcuts via artificial water ways, habitat degradation and environmental pollution are required to reduce the further spread of alien species